How many Mathematicians as good as John Forbes Nash Jr,would there be
in the world appox

If we measure "as good as" by the caliber of the theorems they prove
(and thus John Nash would be measured by his work in algebraic
geometry), an estimate of a hundred or so is probably appropriate.  Of
course, you understand that such estimates are difficult to make, and
some may say less (because of his consideration for the 1958 Fields
Medal) or some may say more.

Cheers.

thankyou very much for your coment.   :)